The solidification and refinement processes of a structure can be controlled effectively by imparting vibration into a melted liquid metal that is to be solidified. For example, it is well known that imparting mechanical impact to a supercooled liquid metal starts the solidification process. It is also well known that imparting vibration to a melted liquid metal creates a fine structure during solidification and applying a compression wave to a melted liquid metal promotes a degasifying process.
On a laboratory scale, it is relatively easy to impart vibratory motion to liquid metal by mechanically vibrating a vessel in which the liquid metal is charged. On a large industrial scale, however, it is difficult to mechanically vibrate the entire structure of a huge vessel. One technique currently used in large scale industrial applications entails, therefore, positioning a magnetostrictive oscillator or an electrostrictive oscillator in a liquid metal to impart a given amount of vibratory motion to the liquid metal. Another such technique entails introducing a compression wave generated by a speaker into a liquid metal to impart a given amount of vibratory motion to the liquid metal.
However, if such a magnetostrictive oscillator or an electrostrictive oscillator is employed, it may be melted or destroyed in and thereby contaminate the liquid metal. The amplitude of the vibration to be imparted is restricted because of oscillator output power level limitations. Moreover, if a compression wave is employed, it may be reflected almost entirely at the boundary between the liquid metal and the surrounding atmosphere and therefore not be imparted to the liquid metal because of an increase in the acoustic resistance between the liquid metal and the surrounding atmosphere. As a result, there is at present no method for propagating vibratory motion into a liquid metal suitable for particular use in large scale industrial applications.